1. Field of the Invention
The present invention relates to wireless communication systems.
2. Description of the Related Art
Communication technology is in a constant state of flux with improvements being made in virtually all aspects of this technology. In particular, wireless communication systems are being designed, built and upgraded to meet ever the increasing demands of their subscribers. One important aspect of wireless communication systems that is currently being upgraded is the capacity—or more importantly, the throughput—of a wireless communication system. Another important and related aspect of the communication system is a system's ability to convey (i.e., transmit and/or receive) information representing not only voice but also data (e.g., graphics, text, digital video). Whether a service provider wants to provide both voice and data or the service provider wants a system with greater capacity, the system throughput has to be improved. It should be well understood that system throughput is the amount of information transmitted and received successfully (without any errors or with an acceptable amount of errors) by system equipment.
The system equipment are the various signal transmitting, signal receiving and signal processing equipment typically used in a wireless communication system. Examples of system equipment include modulators, encoding circuitry, power amplifiers, decoding circuitry, computers, filters and demodulators. A service provider is typically a commercial entity that owns, operates, controls and manages the system equipment. System equipment convey information to other system equipment or to user equipment. Examples of user equipment include cellular phones, pagers, wireless PCs and Personal Digital Assistants (PDAs). The terms “user” and “user equipment” will hereinafter be used interchangeably. In wireless cellular communication systems much of the system equipment is located in base stations that are serving different cells of the communication system. A cell is a geographical area defined by physical boundaries. A base station is formed from one or more locations within a cell and contains system equipment.
One of the critical components of a wireless communication system that directly affects a communication system's capacity and throughput is the antenna equipment used in the system. Antennas transmit and receive communication signals that carry various types of information (e.g., voice, data) throughout the communication channels of the communication system. In order to increase a communication system's capacity and throughput, the number of the antennas themselves has to increase. One technique used for increasing the capacity of antennas is to use a Multiple Input Multiple Output (MIMO) antenna system whereby an array of antenna elements is used to simultaneously transmit and receive communication signals. One example of a MIMO system is the Bell Laboratories Layer Space Time (BLAST) system developed by Bell Labs of Lucent Technologies, headquartered in Murray Hill, N.J. Current antenna systems typically used in wireless communication systems employ a single antenna for a transmitter and a single antenna for a receiver are known as Single Input Single Output (SISO) systems that transmit and/or receive communication signals as per a protocol that is part of an established standard. A protocol is a set of rules for conveying signaling and traffic information over communication channels of a communication system. The protocol is usually part of a standard that is established by standards bodies, industry groups and/or governmental regulatory bodies. SISO systems use one antenna or a one-antenna system to convey information.
Communication signals conveyed between a system antenna and a user of the communication system are transmitted and/or received over communication channels commonly referred to as traffic channels. Associated with each traffic channel are signaling channels (also referred to as control channels) which are used to control the flow of information through the traffic channels in accordance with a protocol that is part of an established standard with which the communication system complies. The information conveyed over the signaling channels are signaling information which control how communications are initiated, maintained and terminated in the traffic channels. Information (signaling and/or traffic) transmitted from system equipment (e.g., base station) to user equipment are said to be transmitted over a forward link. Conversely, information transmitted from user equipment to system equipment are said to be transmitted over a reverse link. Thus, forward signaling information are transmitted from base station to user equipment and reverse signaling information are transmitted from user equipment to base stations.
The format of the signaling information transmitted over the forward and reverse links is governed by the standard being followed by the communication system. Generally, the format of information (signaling and/or traffic) is the particular arrangement of the various portions of that information. A block of signaling information conveyed over a signaling channel relates in some manner to a corresponding one or more blocks of traffic information being conveyed over a traffic channel. The block of signaling information dictates how information flowing through the traffic channel is to be conveyed, processed and interpreted. For example, in a Code Division Multiple Access (CDMA) wireless communication system for 1×-EVDV (EVolution for Data and Voice), the forward signaling information is transmitted over a channel called the Secondary Packet Data Control Channel (SPDCCH). The SPDCCH has a certain format whereby various portions of the signaling information represent how traffic information is to be interpreted and processed.
In a particular version of SPDCCH for example, there are three (3) bits of information called the Encoder Packet Size (EPS) which indicates the number of bits contained in a block of traffic information being conveyed over a traffic channel. The SPDCCH also contains 6 bits called the MAC ID (Medium Access Control IDentifier) which is a particular number that identifies the specific user equipment or mobile conveying the traffic information. The SPDCCH further contains a certain number of bits (usually two (2) bits) called the Redundancy Version (RV) bits which indicate the number of times the same block of traffic information has been retransmitted. When traffic information is transmitted from a base station to a mobile, the base station waits to receive a confirmation message from the mobile indicating whether the mobile has received the transmitted information without errors. If the mobile received the information without errors, it transmits an ACKnowledge (ACK) confirmation message. If the mobile received the information with errors or with an unacceptable amount of errors, it transmits back a Negative ACKnowledgement (NACK) message to the base station informing the base station that the information was received with errors. The base station retransmits the traffic information upon reception of a NACK confirmation message.
The NACK and ACK messages are transmitted over a reverse link channel called the Reverse ACKnowledgement Channel (RACKCH). The base station cannot transmit subsequent traffic information until it receives an ACK or a NACK message from the user equipment. While the base station waits for a confirmation message, it can use that idle time to transmit traffic information to the same user equipment or to other user equipment on a separate channel; in this manner, the base station uses what would otherwise be an idle time period to transmit additional traffic information over other communication channels. The various blocks of traffic information transmitted while waiting for a confirmation message have corresponding ACK or NACK messages associated with them. Two (2) HARQ (Hybrid Automatic repeat ReQuest) bits are currently used to describe the number of communication channels used in transmitting traffic information from the base station to a user equipment; that is, the base station can have up to four (4) traffic information transmissions to one or more users when taking advantage of the idle period that occurs while waiting for confirmation messages.
Another reverse link channel used by user equipment to transmit signaling information to a base station is called the Reverse Channel Quality Indicator Channel (RCQICH). The quality of the forward link communication channels over which the traffic information is transmitted from the base station is obtained by the user equipment. Usually the quality of the forward link communication channels is quantified as the Signal to Noise Ratio (SNR). A mobile is provided with the power level of the noise in the channel and measures the power level of the received signal; the mobile calculates the SNR in a well known fashion using the two power levels. The mobile then transmits the calculated SNR quantity to the base station over the RCQICH.
In communication systems that use MIMO antenna systems, there is a need to have signaling channel formats that can accommodate such systems and are also backward compatible to current SISO systems.